The present invention relates particularly to steerable, battery powered three or four wheeled vehicles of the type used by physically disadvantaged persons and others desiring to ride, and more specifically to new and useful improvements in such vehicles which stabilize them and resist their rearward over-turning when over-tilted upwardly from front to rear for any reason. Vehicles of this type have very significantly improved the quality of life for many people around the world by enhancing their freedom, independence, and mobility, however, it is well recognized that such vehicles must be extremely safe to operate under varied traveling conditions. Because vehicles of this character typically mount a vertically adjustable contour chair on an upstanding post at the rear end of the vehicle so that a relatively high center of gravity load is concentrated at the rear of the vehicle, there is a need to seek to prevent such vehicles from overturning and injuring the passenger, when an adverse tilt occurs.